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Objective:
2D T1-weighted turbo spin echo (T1W-TSE) has historically been the workhorse for contrast-enhanced brain imaging due to its speed and sensitivity to paramagnetic effects. Recently, T1-weighted fluid-attenuated inversion recovery (T1W-FLAIR) has gained popularity due to its greater conspicuity of anatomical detail. However, current literature diverts regarding the performance of these two sequences in terms of sensitivity to contrast enhancement, crucial in the evaluation of brain tumors. The aim of this study is to perform a comparison between T1W-TSE and T1W-FLAIR for the depiction of anatomy and pathology in patients with primary brain tumors.

Materials and Methods:
A total of 110 patients undergoing a clinical brain MRI with a history of primary brain tumor were imaged with both T1W-FLAIR and T1W-SE after a dose of gadolinium-based contrast. 10 patients were excluded due to incomplete imaging, 62 patients for the absence of a primary contrast-enhancing brain tumor and one patient due to motion artifacts. The final sample comprised 32 patients with primary contrast-enhancing brain tumors. Regions of interest (ROIs) were drawn on the most representative slice for tumor enhancement on both T1W-TSE and T1-FLAIR at the same location. Additional ROIs were drawn in a similar fashion on the normal-appearing contralateral white matter (CWM), cortical gray matter (GM), ventricular cerebrospinal fluid (CSF), and perilesional edema (when present). Contrast ratio (CR) for each sequence was evaluated with ratios of tumor enhancement, GM, perilesional edema, and CSF utilizing CWM as reference tissue. Wilcoxon signed rank non-parametric tests were used to establish statistically significant differences.

Results:
A total of 23 patients had a glioma, 18 high-grade (WHO Grade III and IV), and 5 low-grade (WHO Grade I and II). There were also 2 ependymomas, 1 medulloblastoma, 2 primary CNS lymphomas, 2 hemangioblastomas, and 2 mesenchymal tumors. All tumors demonstrated qualitative contrast enhancement both on T1W-FSE and T1W-FLAIR, except one low-grade glioma which demonstrated contrast enhancement solely on T1W-FSE. Differences in T1W-FLAIR and T1W-FSE CR between the enhancing tumor (1.78 ± 0.56 vs 1.80 ± 0.42; T1-FLAIR vs T1-FSE), GM (0.74 ± 0.09 vs 0.93 ± 0.09), CSF (0.07 ± 0.03 vs 0.59 ± 0.15), perilesional edema (0.57 ± 0.23 vs 0.92 ± 0.17) to the CWM were statistically significant (p < 0.01).

Conclusion:
T1W-FLAIR demonstrates a more favorable contrast ratio between white matter, gray matter, and perilesional edema, which are all essential features for evaluating brain tumors. However, T1W-TSE produces higher contrast enhancement ratio between tumors and background brain parenchyma, which is essential for the diagnosis, grading, surgical planning, and evaluation of tumor progression. Differences in tumor enhancement are likely to have more practical implications for patients with hypoenhancing brain tumors, in which contrast enhancement seen on T1W-TSE may be undetectable on T1W-FLAIR. Familiarity with these pulse sequence characteristics is crucial for radiologists designing clinical protocols.