tailieunhanh - Essentials of Neuroimaging for Clinical Practice - part 4

Trục dịch phục hồi đảo ngược giảm độc lực (FLAIR) MRI. rosis). Hình 2-14 trình bày một mô hình MRI FLAIR. Mặc dù dưới vỏ não tổn thương chất trắng trước đây đã quan sát được trên T2W, FLAIR đặc biệt đã nêu bật các tần số mà các tổn thương này được phát hiện tình cờ | Magnetic Resonance Imaging 33 Figure 2-13. Axial proton density PD MRI. Source. Reprinted from Ketonen LM Berg MJ Clinical Neuroradiology 100 Maxims in Neurology Vol. 5 . London Oxford University Press 1997 p. 21. Copyright 1997 Hodder Arnold. Used with permission. signals emanating from normal fluid-filled spaces . ventricles sulci thereby facilitating easier visualization of increased signals emanating from any abnormal parenchymal water content attendant to brain lesions. Hence FLAIR images are useful as the initial scout image for determining whether pathology exists and if so where it exists. FLAIR does not well characterize when the lesions occurred or what they are instead FLAIR s diagnostic power lies in providing a blueprint for use of subsequent sequences to characterize the temporal and pathological nature of the lesions. Clinical Utility FLAIR provides excellent contrast resolution at brain-CSF interfaces lesions that might otherwise be obscured on routine T2-weighted images by high signals from normal adjacent CSF become conspicuous on FLAIR. Edema-generating pathology and white matter lesions including demyelinating processes are especially highlighted with FLAIR. This technique is therefore particularly useful in detecting small incipient demyelination lesions thereby facilitating earlier diagnosis of related disease states . multiple scle- Figure 2-14. Axial fluid-attenuated inversion recovery FLAIR MRI. rosis . Figure 2-14 presents a model FLAIR MRI. Although subcortical white matter lesions were previously observable on T2-weighted images FLAIR in particular has highlighted the frequency with which such lesions are discovered incidentally. Various morphological types exist however when found in seemingly asymptomatic individuals these lesions often consist of multiple scattered punctate subcentimeter hyperintensities that are nonenhancing and are not detectable on diffusion-weighted imaging. The clinical significance of such lesions remains