Materials and Methods
Patients
This retrospective study was approved by our Institutional Ethics Committee.
The radiology information system (RIS) of our institution was searched for patients for whom MRI reports included the keywords of cirrhosis,
chronic liver disease,
DN and HCC between August 2012 and September 2013.
Patients who received dynamic contrast enhanced abdominal MRI with a DW sequence,
age 18 years or older,
and having clinical and / or radiological signs of cirrhosis were enrolled in the study.
Serum AFP levels of patients enrolled in the study were obtained from the medical records of the hospital information system (HIS).
Magnetic resonance imaging protocol
The dynamic contrast enhanced MRI was performed with a 1.5-T superconducting MR system (Signa HDxt,
General Electric Healthcare,
Milwaukee,
USA) with an 8-channel phased-array body coil.
The gradient strength of the system was 50 mT/m and the maximum slew rate was 150 T/m/s.
Breath-hold T1weighted (W) and T2-W SSFSE,
fat suppressed T2-W SSFSE,
T1-W in-phase and out-of-phase images,
3D FIESTA images and gadolinium-based contrast enhanced dynamic 3D imaging with axial LAVA (for arterial phase at 20-35 sec,
for portal venous phase at 60 sec and late images at 180-240 sec) were performed in axial and coronal planes to detect and characterize the lesions for all patients.
Before contrast medium administration,
DW-MRI was performed using a breath-hold single shot echo-planar spin echo sequence on the axial plane.
A total of 20 images were obtained for each patient.
The gradient factors used (b values) were 0 and 800 s/mm².
Image analysis
One of the radiologists,
who searched the RIS,
had collected the clinical data about the patients and images of the lesions investigated.
Later,
the images of the lesions were evaluated by the two radiologists with experience in abdominal imaging of five and ten years according to the criteria established by AASLD guidelines (2,
3).
Both of the two observers were blind to patient identity,
clinical findings and serum AFP level.
Finally,
lesions detected in the liver by dynamic contrast-enhanced abdominal MRI were classified as DN or HCC if they suited the specific criteria set before the image analysis by the consensus of the two observers (Figure 1,2).
The maximum diameter (mm) of the HCC and DN was measured using an axial T2-W SSFSE image as a reference.
The histopathological diagnoses of the lesions were confirmed by searching the HIS.
The SI of DN and HCC nodules were classified as iso,
hypo and hyperintense on DW-MRI at b = 800 s/mm² independently by the two observers and a final decision was reached by their consensus.
ADC values of the DN and HCC nodules were obtained from the ADC maps as the largest and possible regions of interest (ROI) measurements fitted to the lesion on the same workstation by one of the two observers.
The mean of 3 ROI measurements for lesions greater than 2 cm and 2 ROI measurements for lesions smaller than 2 cm were used to obtain ADC values of the same image.
Then the ADC value of normal appearing liver parenchyma (NALP) near to the lesion was measured and the ADC ratio of lesion to NALP was obtained.
Statistical analysis
Nodules were grouped as DN or HCC nodules using dynamic contrast-enhanced MRI or histopathological findings.
The size,
serum AFP levels,
SI on DW-MRI,
ADC and ADC ratio values of DN and HCC nodules were compared with each other by Student T test and Chi-square test.
The Statistical Package for Social Sciences (SPSS version 20.0 Chicago,
IL,
USA) was used to analyse the data.
Numeric data were expressed as mean ± SD or number (percentage),
where suitable.
The size of HCC nodules was compared with serum AFP levels,
ADC and ADC ratio values by Pearson correlation coefficient.
Correlation coefficient values between 0.2 and 0.4 were accepted as weak,
a value between 0.4 and 0.7 as moderate and a value of > 0.7 as strong correlations.
Receiver operating characteristic (ROC) curve analysis was performed to evaluate ADC and ADC ratio values to determine the optimal cut off points for HCC.
Statistical significance was set as p < 0.05 and was bidirectional.