Clinicians and researchers interested in liver tumorLiver functional reserve estimation plays an essential role in making therapeutic decision and predicting the prognosis of patients with hepatocellular carcinoma (HCC). Gd-EOB-DTPA is a hepatocyte-specific contrast agent for MRI which is selectively uptaken by functioning hepatocytes. This study aims to evaluate liver function using the T1 mapping on Gd-EOB-DTPA enhanced MR imaging, and to estimate the correlation with the indocyanine green retention at 15 min (ICG-15).A total of 26 patients (16 male and 10 female; mean age, 55.6 ± 10.3 years) with HCCs proved by surgery were included. ICG-15 was measured in each patient by using Diagnogreen before MR examination. All patients were examined on a Siemens MAGNETOM Skyra 3T scanner (Siemens Healthcare, Erlangen, Germany) with an 18-channel phased-array body coil and spine coil. T1 mapping was acquired using a dual flip-angle 3D gradient-echo sequence with volumetric interpolated breath-hold examination (VIBE) before and 20 minutes after injection of Gd-EOB-DTPA with the following parameters: TE/TR = 1.29/4.00 ms, FA = 2° and 14°; FOV = 380´380 mm2, matrix = 192´154, slice thickness = 4 mm, iPAT = 2. The ROIs (regions of interest) of the liver parenchyma was manually drawn to avoid the areas of visible leisions, the border of the liver, major hepatic veins, and inferior vena cava. T1 values were measured on pre-contrast and during hepatobiliary phase (HBP) on T1 maps. The reduction rate (ΔT1) of T1 mapping between baseline (T1 pre) and HBP (T1 HBP) was calculated as: reduction rate ΔT1(%) = (T1 pre – T1 HBP)/T1 pre×100[1]. The correlation of reduction rate in the liver parenchyma with ICG-15 was assessed by using Pearson’s correlation analysis.Figure 1 showed an example of a liver tumor (a) and its T1 maps before contrast injection (b) and during HBP (c). The T1 values of liver tumor showed higher signals than those for liver parenchyma before contrast injection and during HBP. The reduction rate of the liver parenchyma showed a significant correlation with the ICG-15 (r = -0.610, P <0.001; Figure 2).T1 mapping sequence is used as a method to non-invasive assess liver fibrosis [2, 3]. However, it is rarely reported that T1 mapping is used in liver functional reserve estimation in HCC patients. ICG-15 is a common parameter for preoperative assessment of preserved hepatic function. ICG-15 with a cutoff value of 10% as an upper limit of normal has been widely used in clinical practice in Japan. In the present study, ICG-15 >10% was identified as a preoperative independent risk factor affecting 3- and 5-year recurrence-free survival [4]. In this study, we found that tumors showed clearer borderline on T1 map during HBP. A significant correlation between the reduction rate of liver parenchyma with ICG-15 indicated that the T1 mapping is useful to estimate the liver functional reserve in HCCs patients.T1 mapping on Gd-EOB-DTPA enhanced MR imaging is useful for the liver function estimation in HCCs patients.