Magnetic Resonance: Applications in Dementia
Since MR techniques have become available sensitivity and, to a lesser extent, specificity in the diagnosis of dementias has enormously increased. It is, however, important to use the proper techniques to extract the maximum information from the images an
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Magnetic Resonance: Applications in Dementia
2.1
Magnetic Resonance Techniques
2.1.1
Overview of Available MR Techniques
(Figs. 2.1-1 to 2.1-14) 2.7.7.7 Conventional T7- and T2-Weighted Spin Since MR techniques have become available sensiEcho (SE) Techniques tivity and, to a lesser extent, specificity in the diagnosis of dementias has enormously increased. It is, The main feature of conventional Tl- and T2however, important to use the proper techniques to weighted SE techniques is refocusing of the transextract the maximum information from the images verse magnetization after excitation by a 1800 radioand to answer specific questions. The advantages frequency (RF) pulse. SE sequences are the workand disadvantages of specific techniques must be horses of MR studies and still have value in many known, to minimize the risk of missing a diagnosis cases. Tl-weighted SE sequences give anatomical or reporting incompletely. The available arsenal of detail with a high contrast between white and gray techniques in MRI is impressive and it is rarely pos- matter; pathology is less weil delineated. Tlsible to perform all possible MR techniques in one weighted SE images are also used when Tl-prevasession in one patient, if that were desirable. lent contrast media are used. These contrast media shorten the Tl relaxation time, leading to a high er
Fig. 2.1-1 a, b. Transverse spin echo (SE) images, respectively Tl-weighted (a) and T2-weighted (b). Tl-weighted images show cerebrospinal fluid (CSF) black and give anatomical detail. The lesion in the left caudate region in this image is hypointense and weil defined. On the conventional T2-weighted image CSF is bright as is the lesion on the left side. In the central nervous system pathological tissue often
J. Valk et al., Magnetic Resonance in Dementia © Springer-Verlag Berlin Heidelberg 2002
is hypo- or isointense on Tl-weighted images and hyperintense on T2-weighted images. It is not possible on these two images to conclude whether the lesion is cystic or solid. Therefore one needs to add other sequences. In this case the lesion is solid: a 17-year-old boy with Sydenham's chorea. This one-sided caudate lesion is highly characteristic for the disease
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Fig. 2.1-2 a, b. Transverse turbo (fast) SE T2-weighted image (a) through the level of the mesencephalon and at about the same level a FLAIR (dark fluid) image (b) in a patient with an asymmetrical cortical degenerative syndrome. Both images show the predominant left temporal lobe degeneration, with widening of the temporal horn, loss of structure
in the hippocampus, signal changes in the white matter of both temporal lobes on both sides, worse on the left, and irregular cortical atrophy, also more conspicuous on the left side. The FLAIR image highlights the gliotic part of the white matter changes in the temporal pole
signal where the blood-brain barrier is disturbed. Conventional T2-weighted sequences provide less contrast between gray an
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