Patient and tumor characteristics
Twenty-six patients with solid liver lesions were included in this study, consisting of 10 cases of HCC (7 male, 3 female, aged 45–75 years old [mean age 58.8 years]) and 16 cases of CRHM (11 male, 5 female, aged 48–67 years old [mean age,61.3 years]). In HCC patients, the diagnosis was either histologically confirmed during surgery (n = 8) or based on dynamic CT findings together with high serum α-fetoprotein (n = 2). Cirrhosis was confirmed in all patients with HCC (Child-Pugh A: 9, B: 1), either through pathological assessment or clinical and imaging criteria. Of the 16 CRHM patients, four cases were histologically confirmed during surgery. Twelve cases showed significant growth or regression of lesions at follow-up imaging after the commencement of chemotherapy (defined as ≥20% diametric growth or regression, mean time of follow-up 4.2 months with a range of 2–6 months). All patients were required to not have received any therapy prior to inclusion. In each patient, a single lesion was chosen as study target, which were required to be well demarcated contrast-enhancing solid masses larger than 1.5 cm in the longest diameter. This study was approved by the ethics committee of Zhongshan Hospital, Fudan University (Approval No:2010-17) in compliance with the Helsinki Declaration, and written informed consent was obtained from the patient for publication of this report and any accompanying images.
Perfusion MR imaging
The patients were asked to fast for 6 hours before imaging. Perfusion MR was performed using a 3.0-T system with phased-array coils (Verio, Siemens Medical Solutions, Erlangen, Germany). For T1 map calculation, a dual flip angle (FA) 3D gradient echo sequence with volumetric interpolated breath-hold examination.
(VIBE) was performed preceding injection of contrast material. The following imaging parameters were used: 2.84/1.02 (repetition time msec/echo time msec), 2° and 9° FA, 134 × 256 matrix, 2.5 × 1.5-mm in-plane pixel size, 380 × 333-mm field of view, 20 cm slab thickness resulting in an interpolated 5-mm section thickness, and 750 Hz/pixel bandwidth. A parallel imaging technique (R factor of two) was performed using generalized autocalibrating partially parallel acquisition. Whole-liver perfusion MR imaging was performed by VIBE in the coronal plane using 9° FA. The geometrical and spatial parameters of the perfusion series match the pre-contrast sequence (resolution, dimensions, orientation) with a temporal resolution of 3.7 seconds. The first “breath-hold” lasted 1 scan, which was aligned with the beginning of contrast material injection to obtain a baseline scan. At the 16th second, three subsequent “breath-holds” were orchestrated, each lasting for 5 scans every 8 seconds. Finally, 4 subsequent “breath-holds”, each accounting for 4 scans were obtained in 12-second intervals, resulting in the acquisition of a total of 32 scans (Figure 1). All patients received 0.1 mmol/kg body weight of gadopentetate dimeglumine, administered intravenously at 5 mL/s through a cubital or cephalic venous entry, and flushed with 20 mL 0.9% saline.
Data analysis
MR images were analyzed by using commercially available software on a separate workstation (Tissue 4D, Syngo MR B17, Siemens Healthcare) to calculate the perfusion parameters. Semi-automatic evaluation of hepatic tumors was performed by two radiologists experienced in abdominal MR imaging, who separately and independently evaluated the hepatic tumors. The following algorithm was applied: 1. Motion correction: selection of the the first volume of the dynamic series as reference volume. The new motion-corrected series automatically replaces the original dynamic series; 2. Registration: selection of the first volume in the dynamic series as reference volume for registration; 3. Curve calculation: calculation of enhancement curves and segment structures manually by drawing regions of interest (ROIs) in the dynamic series. The curves are shown as relative enhancement curves with the first volume serving as reference. 4. Pre-evaluation: the T1 map calculation of pre-contrast data is a prerequisite for pharmacokinetic modeling. It runs automatically when we start the pre-evaluation blind. T1 fitting is restricted to pixels with values above the noise level cutoff. Once the T1 map is calculated, the pre-contrast is replaced; 5. Evaluation: the Evaluation blind allows pharmacokinetic modeling of the mean curves for the selected ROI label. The two-compartment Tofts model of arterial input functions (AIFs) is provided; 6. Results: the ROI functionalities on the Results blind comply with the functionalities on the Curve Calculation blind. The setting affects only the ROIs displayed in parameter images (Figure 2); 7. Export: export of the results.
Statistical analysis
Inter-observer variation for perfusion parameters (Ktrans, Ve, and Kep) was analyzed using a Bland-Altman plot. Mann–Whitney test and independent samples t-test were conducted to analyze the difference in mean parameter values between HCC vs. CRHM patients. All statistical analyses were conducted using MedCalc (MedCalc for Windows, version 9.6.4.0). A p-value of less than 0.05 was considered significant.