The administration of gadolinium contrast agent (Gd) is an important part of MR imaging examinations in patients with brain metastases for the diagnosis and monitoring of disease progress. Leakage of Gd into brain tissue changes the absolute magnetic properties of tissue water, strongly reduces the T1 relaxation, resulting in hyperintensity on T1-weighted images. This effect may even vary with the timing of contrast administration. Synthetic MRI is a method to generate conventional images based on MR quantification and enable quantitative measurements with relatively short times.1, 2 It is insensitive to both MR-scanner hardware and MRI acquisition protocol. By now, there is no study which evaluate the effect of contrast agents on the T1 shortening in the brain metastases by using synthetic MRI with different timing of image acquisition after contrast injection. Therefore, the objective of this study was to determine the optimal acquisition delay for quantitative imaging of brain metastases with contrast-enhanced synthetic MRI.A cohort of 7 patients with 15 brain metastases were recruited, quantitative MRI sequence was acquired before (dT0) and after the administration of Gd at 3T. A 2D fast spin echo(FSE) multi-dynamic, multi-echo (MDME) sequence, which was performed using an interleaved slice-selective 120 degrees saturation and multi-echo acquisition was used. They obtained three different delay time points after the administration of contrast agent: immediately (dT1 map), 8 minutes (dT2 map) and 20 minutes (dT3 map) (Figure). Synthetic images were created using SyMRI Diagnostics (SyntheticMR AB, Linko¨ping, Sweden). ROIs containing the enhancing portion of the tumor were drawn on every section of three postcontrast T1 maps to derive volume-based data of the enhancing portion of the tumor. In addition, ROIs that contained the entire tumor were drawn in each section of the three postcontrast T1 maps and ROIs on the dT3 maps copied to the precontrast dT0 maps. The median, skewness and kurtusis were derived from the histograms of T1 maps. The Kruskal-Wallis test with post-hoc analyses was used to compare the parameters values between dT0, dT1, dT2 and dT3 maps. In addition, lesion volumes (ml) were compared between dT1, dT2 and dT3 maps. Regression was used to describe the relationship between the delay times and several parameters. The median and skewness of the T1 value of the brain metastases on the dT0 were significantly different from those on the three postcontrast maps (P = 0.0001, P = 0.004, respectively) (Table 1). However, there was no significant difference and relationship in the parameters between the dT1, dT2 and dT3 maps (P > 0.05) and the lesion volume between dT1, dT2 and dT3 maps (P > 0.05) for both enhancing portion of the tumor and whole tumor (Table 2).There was no optimal acquisition delay for postcontrast quantitative MRI of brain metastasis. Postcontrast quantitative MRI can be acquired regardless of time within 20 minutes after the contrast administration.