This study was approved by our institutional review board, and informed consents were obtained from all patients before MRI examinations. We included the patients who: (1) had no previous history of biopsy, surgery or any other treatment; (2) underwent conventional MRI and DWI for pre-treatment evaluation of sinonasal tumors; (3) had an adequate MRI quality without motion and susceptibility artifacts; (4) had a final pathological diagnosis of sinonasal SCC or NHL. Finally, a total of 21 patients (male: female = 11:10; mean age, 61.4 ± 12.7 years) with sinonasal SCC and 15 patients (male: female = 8:7; mean age, 59.9 ± 17.9 years) with sinonasal NHL (9 with NK/T lymphoma, 6 with diffuse large B cell lymphoma) were included.
MRI was performed using a 3T scanner (Verio, Siemens Healthcare Sector, Erlangen, Germany) with a 12-channel head and neck coil. MRI protocol included the following sequences: unenhanced axial T1-weighted imaging (TR/TE = 811/7.1 ms, section thickness = 4 mm, field of view [FOV] = 220×220 mm, matrix = 384×384); axial T2-weighted imaging with fat saturation (TR/TE = 4000/87 ms, section thickness = 4 mm, FOV = 220×220 mm, matrix = 384×384); coronal T2-weighted imaging (TR/TE = 3800/88 ms, section thickness = 4 mm, FOV = 220×220 mm, matrix = 384×384), and contrast-enhanced axial T1-weighted imaging (CE-T1WI) (TR/TE = 811/7.1ms, section thickness = 4mm, FOV = 220×220mm, matrix = 384×384). For CE-T1WI, a standard dose of 0.1 mmol/kg of gadolinium-diethylene triamine pentaacetic acid (Omniscan, GE Healthcare, Dublin, Ireland) was administrated at a rate of 4 mL/s, followed by a 20 mL normal saline
Readout-segmented echo planar imaging sequence (RESOLVE) was used for DWI scan. Detailed imaging parameters were showed as follows: diffusion schema, Stejskal–Tanner; fat suppression, frequency selective; b values, 0 and 1000 s/mm2; orthogonal directions, 3; TR/TE, 5060/76 ms; slice number, 20; number of excitations, 1; FOV, 220×220mm; slice thickness, 4 mm without gap; matrix, 224×224; phase-encoding direction, anteroposterior; echo spacing, 0.4 ms; number of readout segments, 5. Total acquisition time of DWI based on RESOLVE technique was 2 min 45 s.
MR images were analyzed by two radiologists (with 7 and 3 years of experience in head and neck radiology, respectively) who were blinded to the study design and pathological information. T2WI and ADC map were registered to the CE-T1WI. ROIs were manually drawn in dedicated image processing software (FireVoxel; CAI2R; New York University, NY) with a filtration-histogram approach . Tumor ROIs were manually delineated around all the slices on T2WI, ADC and CE-T1WI (Figure 1). Three-dimensional (3D) volumes of interest (VOIs) were constructed by summing ROIs drawn in each section. Large necrotic, cystic or hemorrhagic areas were carefully avoided with reference to T2WI and CE-T1WI. Lastly, volumetric regions were isotropically resampled to the in-plane resolution (voxel size = 1×1×1 mm) using cubic interpolation to ensure the conservation of scales and directions when deriving the 3D features . After the VOIs were placed, following quantitative texture parameters were automatically obtained: mean value, skewness, kurtosis, uniformity, energy and entropy, which are based on histogram analysis and the gray-level co-occurrence matrix (GLCM) method .
Numeric data were averaged over all patients, and reported as mean ± standard deviation. Data normality was tested by using the Kolmogorov–Smirnov test. Fisher’s exact test was applied to assess the difference of binary variables between two groups. Texture parameters were compared between two groups using unpaired Student’s t-test or Manne-Whitney U-test as appropriate. Receiver operating characteristic (ROC) curves were performed to assess the performance of each significant texture parameter in the differential diagnosis between sinonasal NHL and SCC. Area under the ROC curve (AUC), sensitivity, and specificity were calculated. All of the significant TA parameters were stepped into a multivariate logistic regression analysis to identify the independent parameter for differentiating sinonasal NHL from SCC. Inter-reader agreement was evaluated using intra-class correlation coefficient (ICC) with 95% confidence intervals, and classified as excellent (ICC ≥ 0.81), good (ICC = 0.61-0.80), moderate (ICC = 0.41-0.60), and poor (ICC < 0.40). All statistical analyses were performed by using MedCalc (version 13.0; Mariakerke, Belgium) and SPSS (version 24.0; IBM Corp., Armonk, NY, USA). A two-sided P value less than 0.05 was considered to be statistically significant.