MR Imaging of Posterior Fossa Infarcts: FLAIR vs T2-weighted Sequences
Background and Purpose: Fluid-attenuated inversion-recovery (FLAIR)imaging sequences are generally thought to provide superior lesion contrast over T2-weighted sequences in MR imaging of nonacute ischemic infarcts. To evaluate whether this applies to lesions in the posterior fossa in particular, we compared the conspicuity of posterior fossa infarcts negative on diffusion-weighted imaging between FLAIR and T2-weighted sequences. Methods: Administrative and Radiology databases were used to identify neurology outpatients at a tertiary care center who underwent brain MRs in 1999 demonstrating brainstem infarcts. Contrast-to-Noise Ratios (CNR = (Slesion - Sbackground)/SDair))were computed for the lesions on the axial fast spin echo T2-weighted and FLAIR images. Lesion conspicuity was qualitatively compared between the two imaging sequences by two stroke neurologists unaware of the study question. Results: There were 8 pontine and 13 cerebellar infarcts identified on 19 brain MRs. Mean repetition and echo times were 3537 (SD±122) and 93 (SD±3), respectively, for the T2-weighted images and 7143 (SD ±1014)and 105 (SD ± 0) for the FLAIR images. The mean Contrast-to-Noise Ratio was significantly higher in the T2-weighted images (26.3, SD ±18.9) than the FLAIR images (2.4, SD ±4.3) (p< 0.001). Conspicuity was judged to be superior on the T2-weighted images significantly more often by both stroke neurologists (86%, 95%, p= 0.001). Conclusion: T2-weighted images may provide better lesion contrast in nonacute posterior fossa infarcts than FLAIR images. Careful attention to the T2-weighted images may assist in the detection of nonacute pontine and cerebellar ischemic infarcts.