Relationship between contrast enhancement on fluid-attenuated inversion recovery MR sequences and signal intensity on T2-weighted MR images: Visual evaluation of brain tumors

Purpose To investigate the relationship between the degree of contrast enhancement in fluid‐attenuated inversion recovery (FLAIR) sequences and tumor signal intensity on T2‐weighted images. Materials and Methods A total of 96 patients suspected of having brain tumors were examined by MR imaging, and whenever a brain tumor with an enhancing part larger than the slice thickness was demonstrated on postcontrast T1‐weighted images, postcontrast FLAIR images were additionally acquired. The tumor signal intensity on the T2‐weighted images was visually classified as follows: equal or lower compared with normal cerebral cortex (group 1), higher than normal cortex (group 2), and as high as cerebrospinal fluid (CSF) (group 3). When a lesion contained several parts with different signal intensities on T2‐weighted images, we assessed each part separately. In each group, we visually compared pre‐ and postcontrast FLAIR images and assessed whether tumor contrast enhancement was present. When contrast enhancement was present on FLAIR sequence, the degree of contrast enhancement in T1‐weighted and FLAIR sequences was visually compared. Results Postcontrast T1‐weighted images showed 46 enhancing lesions, including 48 parts, in 31 MR examinations. FLAIR images of the lesion‐parts in group 1 (N = 18) did not show significant contrast enhancement. In group 2 (N = 12), all the parts were enhanced in FLAIR sequences, and three parts were enhanced more clearly in the FLAIR sequences than in the T1‐weighted sequences. In group 3 (N = 18), all the parts were enhanced equally or more clearly in the FLAIR sequences than in the T1‐weighted sequences. Conclusion The signal intensity in FLAIR sequences is largely influenced by both T1 and T2 relaxation time; there is a close relationship between the signal intensity of brain tumors on T2‐weighted images and the degree of contrast enhancement on FLAIR sequences. When tumors have higher signal intensity than normal cortex on T2‐weighted images, additional postcontrast FLAIR imaging may improve their depiction. J. Magn. Reson. Imaging 2005;21:694–700. © 2005 Wiley‐Liss, Inc.