Participants
The study was approved by the Ethics Committee of Shanxi Provincial People's Hospital (Fifth Hospital of Shanxi Medical University). A total of 83 patients with brain lesions were enrolled from December 2020 to May 2022. Inclusion criteria were: (1) patients with a definite diagnosis; (2) patients eligible for MRI, and who underwent MRI imaging preoperatively. Those who underwent chemotherapy or radiation therapy were excluded. All gliomas were diagnosed by surgical pathology (n = 54) according to the WHO 2016 Classification [24]; the diagnosis of SBM was obtained from histology (n = 29), imaging follow-up of malignant tumor metastasis (n = 2), or tumor markers from laboratory tests (n = 4) [25]. In addition, 18 patients were excluded prior to the analysis due to the following reasons: incomplete imaging data (n = 10) and/or unsatisfied image quality (i.e., significant cystic, hemorrhagic, or massive tumor necrosis; n = 8). The remaining 65 patients were included in the study, and the study flowchart is shown in Fig. 1.
Data Acquisition
MR sequences including T1WI, T2WI, T2 fluid-attenuated inversion recovery (FLAIR), IVIM, DWI, APT weighted imaging (APTWI), and enhanced T1WI were conducted in a 3.0T MR scanner (Discovery MR 750W, GE Healthcare, Waukesha, WI, USA) with a 24-channel head neck unit coil. Axial IVIM used 12 b-values (0, 20, 40, 80, 110, 150, 200, 400, 800, 1200, 1500, and 2000s/mm2). The following parameters were applied: repetition time/echo time (TR/TE) = 5400ms/90ms, the field of view (FOV) = 220×220mm, matrix size = 110×110, slice thickness = 4.0mm, intersection gap = 1.0mm. The parameters for axial DWI with b-values of 0 and 1000s/mm2 were: TR/TE = 6000ms/76ms, FOV = 240×240mm, matrix size = 120×120, slice thickness = 4.5mm, intersection gap = 1.0mm. Diffusion gradients were applied in three orthogonal directions for both IVIM and DWI, and the scanning slices covered the area of the whole lesion. The APTWI was acquired using a 2D single-shot fast spin-echo-based sequence (TR/TE = 2950ms/27ms, FOV = 256mm×256mm, matrix size = 120×120, slice thickness = 8mm) with phased cycle pulses for saturation and the water saturation sift reference (WASSR) for B0 correction. The total duration for phase cycle pulses is 2000ms under B1 of 2\(\mu\)T. The Z-spectra includes 52 frequencies, 49 of which offset from 600 to -600 Hz at an interval of 25 Hz, and three unsaturated images at 5000 Hz for signal normalization. The maximum slice without or with a minimum area of hemorrhage and cyst in axial T2FLAIR was selected for ATPWI data acquisition.
Imaging Processing
The DWI, IVIM, and APTWI images were imported to the iQuant software (GE Healthcare, Beijing, China) to calculate the parametric maps. The DWI apparent diffusion coefficient (DWI-ADC) was generated with the formula:
Sb/S0 = exp (-b × ADC) (Eq. 1)
where Sb and S0 were the signal intensities for b = 1000 s/mm2 and b = 0 s/mm2,. The IVIM data were processed with the bi-exponential model as defined by the equation:
Sb/S0 = f × exp (-b × D*) + (1-f) × exp (-b × D) (Eq. 2)
where Sb is the signal intensity under b > 0 s/mm2, D* is the pseudo-diffusion coefficient, D is the true-diffusion coefficient, and f represents the perfusion fraction. The APTWI asymmetric magnetization transfer ratio at 3.5 ppm is represented as MTRasym (3.5 ppm) and calculated by:
MTRasym (3.5 ppm) = [Ssat (− 3.5 ppm) − Ssat (+ 3.5 ppm)]/S0 (Eq. 3)
where the S0 is non-saturation intensity while Ssat is the signal intensity after saturation.
Y.H (a neuro-radiologist with 30 years of work experience) delineated the region of interest (ROI) on tumor parenchyma with the enhanced T1W image as the reference where the cerebrospinal fluid-filled, calcification, hemorrhagic, necrotic, and cystic areas were avoided wherever possible in 3D-Slicer (https://www.slicer.org/, version 4.10). For IVIM and DWI, ROIs were drawn slice by slide, and a 3-dimension ROI was eventually obtained, while for APTWI, a 2-dimension ROI was acquired since only one slice of imaging was acquired. The first-order and histogram features, including mean, 10th percentile, 90th percentile, entropy, kurtosis, and skewness for all parametric maps in tumor ROIs were extracted with the pyradiomics plugin (https://pyradiomics.readthedocs.io/).
Statistical analysis
Quantitative variables were expressed as the mean ± standard deviation and were compared with the Student's t-test or the Wilcoxon test (Mann-Whitney U test) after the normality and homogeneity of variance were confirmed. The binary data for clinical information were compared using the Chi-Squared test. Next, the variables with significant differences were assessed using univariate and multivariate logistics regression. The receiver operator curves (ROC) analysis was applied to explore the performance of independent factors and multi-parameter combined models for differentiation of glioma and SBM. The area under the ROC curve (AUC), sensitivity (sen.), specificity (spe.), positive predictive value (PPV), and negative predictive value (NPV) were calculated and compared. Nomogram and bootstrap resampling methods were used for the evaluation of the multivariate logistics regression. R package (version 4.0.0) was used for all the statistics. A P value < 0.05 indicated a statistically significant difference.